Former U.S. Attorney General John Ashcroft is testifying at a Congressional hearing on interrogations of suspected terrorists, including those being held at Guantanamo.

Ashcroft told the hearing in his opening statement Thursday that after the September 11 terrorist attacks in 2001, the Bush administration's goal was to do everything in its power and within the limits of the law to keep the U.S. and its people safe from terrorist attacks.

He said he believed the United States has disrupted a number of terrorism plots since the September 11 attacks. He said this suggests that some, but not all, of the techniques the U.S. is using are right.

Benjamin Wittes, a terrorism analyst, told the hearing that the Central Intelligence Agency, like the military, should have its own list of approved interrogation techniques. He said these techniques should be approved by Congress and open to public scrutiny.

Wittes argued the CIA's current guidelines are too vague.

Former assistant attorney general and solicitor general Walter Dellinger also is testifying at the hearing.

He said he does not think the United States wants to be a country that officially approves the use of cruelty. He also said he thinks the president does not have the lawful authority to pardon someone in advance for what would be a criminal offense. The Bush administration has sought to have immunity granted to interrogators.

U.S. methods of interrogating terror suspects have included waterboarding, a partial drowning technique that, in the past, the government has considered torture.

About 275 prisoners remain at the prison at Guantanamo Bay, Cuba, some of whom have been held for six years without a court hearing.

Last month, the U.S. Supreme Court ruled that detainees at Guantanamo have a right to challenge their detention in U.S. civilian courts. Despite that ruling, Attorney General Michael Mukasey said military trials for suspected terrorists at the military prison will proceed.